1. Field of the Invention
The present invention relates to a novel optically active compound useful as a chiral dopant, a liquid crystal composition containing the compound and a liquid crystal display device to which the liquid crystal composition is applied. More specifically, it relates to a chiral dopant having a helical twisting power (HTP) of at least 9 and having the property that a helical pitch induced by the chiral dopant decreases with an increase in temperature, and use thereof.
2. Prior Art
Various modes are known as display modes of liquid crystal display devices, and in most of such display modes, it is required to control the helical pitch of a liquid crystal. The mode that requires control of the helical pitch of a liquid crystal includes the following modes.
The modes that have been put to practical use and widely employed are a twisted nematic mode (TN mode) and a super twisted nematic mode (STN mode) using a nematic liquid crystal.
In the TN mode, liquid crystal molecules are aligned so as to twist at 90 degrees between an upper substrate and a lower substrate, and a xc2xc pitch of a helix is formed in a cell.
In the STN mode, liquid crystal molecules are aligned so as to twist at approximately 220 degrees between an upper substrate and a lower substrate, and an approximately ⅗ pitch of a helix is formed in a cell.
The TN mode is employed in a simple matrix driving liquid crystal display device and an active matrix driving liquid crystal display device, and the STN mode is employed in a simple matrix driving liquid crystal display device.